3-wire power: twist or braid?

[JeffYoung]

For instance:

+, -, and ground from a PSU to a channel board,
​

or

+, out, and ground from a CCS
​

Twist them or braid them, or will either do?

 

[fabrice63]

what ever happens , make them short , very short


.

 

[DF96]

Twist.

Braiding is used when a single flexible connection is required, with reasonably low inductance. Or when appearance matters, as in some hairstyles.

 

[AndrewT]

Twisted triplet has lower LOOP AREA than any other 3wire arrangement.

It's LOOP AREA that makes for a better EMI emitting aerial.

Think of the output from a PSU as +veVolts and 0Volts and -veVolts, not ground.

 

[JeffYoung]

That's kind of what I figured. Having never braided (hair either), I was kind of looking forward to trying it out, but twist it will be.

Cheers,
Jeff.

 

[scottjoplin]

Have you wondered why twisting is better? Besides what Andrew said

 

[Chris888]

If your system is really +ve, +ve return, -ve and -ve return, it may be better to put in two GND wires and twist +ve and -ve circuits separately.
If the current is really flowing from +ve to -ve andd GND is just a reference, it may be better to twist +ve and -ve, then wind GND around it.
If it makes that much difference, you are sailing close to the wind....

 

[JeffYoung]

If your system is really +ve, +ve return, -ve and -ve return, it may be better to put in two GND wires and twist +ve and -ve circuits separately.
If the current is really flowing from +ve to -ve andd GND is just a reference, it may be better to twist +ve and -ve, then wind GND around it.
If it makes that much difference, you are sailing close to the wind....

They're both sort of in the middle. The CCS uses GND only as a reference, but the load is so small that the reference current is 50% of the load current!

In the PSU case the signal current goes from +23V or -23V through the load to 0V, while the quiescent current goes +23V to -23V (with only the locally-filtered ripple going to 0V).

 

[AndrewT]

They're both sort of in the middle. The CCS uses GND only as a reference, but the load is so small that the reference current is 50% of the load current!

In the PSU case the signal current goes from +23V or -23V through the load to 0V, while the quiescent current goes +23V to -23V (with only the locally-filtered ripple going to 0V).

It not just signal currents that need to return to source.
Interference, noise and the unbalance of the rail quiescent currents will probably return to the source via the zero volts connection.
If any of these varying currents pass around a loop they will emit EMI.
Constant level DC cannot emit EMI. Varying level DC is a varying current and will emit EMI.

 

[AndrewT]

If your system is really +ve, +ve return, -ve and -ve return, it may be better to put in two GND wires and twist +ve and -ve circuits separately.
If the current is really flowing from +ve to -ve andd GND is just a reference, it may be better to twist +ve and -ve, then wind GND around it.
If it makes that much difference, you are sailing close to the wind....

A power supply that is +ve and -ve is a single polarity supply.
The supply sources a current and must by the laws of nature sink that same current.

Where there is a Zero Volts line from a dual polarity supply, then some current will return to source via the Zero Volts line. This requires that the returning current be close coupled to the source line to minimise EMI.